Dustmite is a tool written by CyberShadow that ships with the stock DMD download. It is a bug reducer.
Have you ever run into a compiler bug? Or some error message that you didn't understand, because it involved too much source code? Have you formed a theory about what was its cause, only for your simple testcase to end up unable to reproduce it? How does everybody else make those nice, simple testcases anyways? The answer is Dustmite.
How does that work? In fully general terms, Dustmite takes two things: a test folder, and a tester.